DE2844333A1 - ARRANGEMENT FOR CORRECTING GRID COVERAGE ERRORS IN A TELEVISION CAMERA - Google Patents

Description

RCA 72 273 Ks / Ki

US Serial No: 841,196 ^ u.
Filed: October 11, 1977 -τ *

ECA Corporation
New York, NY, V. St. v. A.

Arrangement for the correction of grid registration errors in a

TV camera

The invention relates to an arrangement which ensures that in a television camera from several image recording devices generated grid come into congruence with each other.

Many of today's television cameras contain two or more image capture devices for obtaining video signals which contain the image information of the recorded scene. In such Cameras are separate means in the form of deflection devices for each of these individual recording devices (mostly recording tubes) and assigned deflection signal generators in order to scan the respectively recorded image in a raster and thus a raster-related one Signal to receive. Through mechanical and physical alignment and through precise selection or adaptation of the image pickup tubes with regard to their deflection sensitivity and the deflection devices and the associated deflection signal generators one tries to match the raster-related signals coming from the individual image pick-up tubes as well as possible with one another bring. Despite the greatest care, it is practically not possible to achieve the desired grid coverage without any additional ones Measures for fine adjustment of certain grid parameters to achieve, including in particular the centering, the width, the height, the linearity, the rhombus error and the rotation of a Rasters belong to the other, which are related to an internal

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half of the same camera optically projected scene in accordance are to be brought.

Camera systems have been developed which have both a local and a remote-controlled normal setting of the aforesaid Allow parameters. However, such adjustments are time-consuming and require frequent readjustments in order to achieve a satisfactory Maintain coverage of the individual grids in a television camera operating with multiple image capture devices.

Automatic systems for correcting misregistration are therefore desirable and such systems are well developed been. In general, in the known methods of automatic misregistration correction, a test image of the Camera recorded, and the video signals derived from each image pickup tube are based on phase or time shifts compared to.

A common phase detector, generally as a level comparison circuit is formed, compares a sweeping video signal with a reference voltage level to determine the position of one of the raster-related video signals relative to the other takes raster-related video signals. That is, the leading or trailing edges of the video signals are determined and compared, whereupon an error signal is generated which is related to the displacement the video signals. Usually, however, the typical forms of video signals from various image recording devices, looking at a test image or a scene are not completely the same, since the video signals do not change with the sudden changes in the image reproduce an ideal square waveform but a peak amplitude with very different rise and fall delays.

A conventional detector is therefore incapable of accurately determining the required point of the peak amplitude of each frame-related signal by determining the coincidence of the leading or trailing edges of the various video signals.

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More complicated detectors have been developed in which multiple erotes of overlap of both the fore and the trailing edge can be taken with a special reference pattern, whereupon by means of an electronic calculator and a complicated one Erogramm the peak amplitude is determined in order to determine the difference between the raster-related video signals.

However, the systems described above for automatic coverage control have not found widespread use, because although if the adjustment happens automatically, the devices for sensing the misregistration of a grid work opposite another grid either not accurate enough or, as in the case of the more complex detectors, increases the complexity and the cost of the automatic system excessive.

The present invention provides a system for establishing or maintaining grid registration in a television camera created, which contains at least two image recording devices and devices for forming associated television raster, the each other in their mutual position with regard to a common, can distinguish the scene depicted on the recording devices. The system includes a device to get into the gaze path of the image recording devices to introduce a common reference object which has a first and a second boundary and which Brings image recording devices to generate a first or a second raster-related signal. A facility is provided in order to select at least one line which is common to the television rasters and which contains the raster-related signals, their amplitude increases from the first limit to a peak amplitude between the two limits and from this peak amplitude to the second Falls towards the limit. The system also includes a device for setting a common time reference on the aforesaid common television line, which is temporally and spatially "in front of" the common reference object. A clock provides one first and second reference frequencies. A first and a second signal transmission channel each speak to a signal detector

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on the first and the second raster-related signal to a generate first and second gating signals, respectively, when the first and second raster-related signals exceed a given reference level. A first and a second counter are included coupled to the first and the second reference frequency and speak to the common time reference signal and to the first and the second gate your signal to the periods of the first frequency from the common time reference to the first and second gating signals and the periods of the second frequency during to count the duration of the gate control signals, the sum count value of the first and the second counter being the position of the peak amplitude of the grid-related signals relative to the common time reference. With the first and second counters is one Control device coupled, which is based on the total count in the first and the second counter is responsive to generate a control signal indicative of the difference in position of the television raster. With An arrangement is coupled to the raster-forming devices which, under the influence of the control signal, the difference between the Ra s t erp o s it i ons diminished.

The invention is illustrated below using exemplary embodiments explained in more detail by drawings.

FIG. 1 shows the block diagram of an arrangement according to the invention to correct Easter coverage errors,

Figures 2, 3a to 3b, 4a to 4b show waveforms for illustration the mode of operation of the arrangement according to FIG. 1;

Figure 5 is a block diagram of one embodiment of a grid coverage detector according to the invention;

FIGS. 6 and 7 show typical reference patterns which are used for realization of the invention can be used;

FIG. 8 shows the block diagram of another exemplary embodiment for an Easter coverage detector according to the invention.

In the figure 1 is a card 100 with an Eeferenz-

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Shown pattern that consists, for example, of a white bar 110 on a black background. This reference pattern is arranged in the line of sight CC of a television camera 120. The card with the reference pattern can alternatively also be brought into the viewing path CC by inserting it within the lens system, as indicated ^{by the dashed line DD 1.}

The television camera 120, which can be a typical color television camera with, for example, three image pick-up tubes and associated raster-forming circuits 160, generates three video output signals VVj, Vq and Vg for the red, green and blue image extracts of the scene seen in view path CC. Since the reference image card 100 lies in the common line of sight CC of all three image pickup tubes and since normal white contains equal proportions of red, green and blue colors, the video output signals Vtj, Vg and Vg represent waveforms which are characteristic of the position of the three color-related rasters. That is, if the grids of the three image pickup tubes are not the same size or are not completely congruent with one another, then there are position or time differences between the waveforms of the signals belonging to the individual grids.

A grid coverage detector 130 senses it below will be explained in more detail, the difference in position of the three video signals and provides an error signal at its output, which is fed to a processing device (control signal generator) 140 will. This control signal generator 140 determines the measure and the direction of misregistration of each raster-related signal by using one of the raster-related signals, e.g. the green signal, used as a reference. The amount and direction of the coverage error the red signal compared to the green signal and the blue signal compared to the same green signal therefore result in two control signals, which show the offset of the red and blue grids with respect to the green grid.

The red grid difference signal and the blue grid difference signal from the output of the control signal generator 140 are then coupled to a raster correction signal generator 150 of known type, the

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Output variable is fed to the raster-forming circuits 160, in which e.g. the centering of the "blue and red basters" is adjusted so that it coincides with the green Easter and thus the misregistration of the Easter due to centering errors is eliminated.

Similarly, Easter correction signals starting with With the help of the control signal generator, other parameters of the Easter such as height, width, linearity and ehombus error can also be formed adjusted.

The arrangement shown in FIG. 1 and generally described above thus forms a closed loop for the automatic control of the baster coverage, the accuracy of the coverage achieved almost entirely depending on how exactly the branch coverage detector 130 positions or time differences in the video output signals Vn, Yn and Vn can feel. FIG. 2 shows typical forms of the course of a video signal which is derived when the scanning beam of a pickup tube crosses the image of a reference pattern lying in the viewing path. The waveform a in FIG. 2 shows an ideal course of the video signal when the beam crosses the border from completely black to completely white. However, since the beam spot has a finite size and the recording system does not have an infinitely large bandwidth, the typical signal curve corresponds more to waveform b in Figure 2.If, for example, the beam from the image pickup tube is defocused, the resulting aperture distortion is greater, so that the output video signal has more corresponds to waveform c in FIG.

It is seldom possible by adjusting or selecting the image pickup tubes ensure that the individual video signals from a multi-tube camera are all equal to each other, i.e. all of the with the waveform b or with the waveform c shown in FIG. In practice you will be more likely to use a combination of the various waveforms shown. From Figures 3 and 4 it can be seen that then the conventional edge detectors as mentioned above are unable to accurately locate the desired peak position of the video signals

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3a shows how two video signals A and B, which are shifted from one another according to FIGS If waveforms A and B are oriented on the leading edge and a conventional leading edge detector is used for this purpose, then the vertex t of waveform A will come to lie in front of vertex t- of waveform B, as shown in FIG the Eückflanke detected, the vertex of the waveform A to the vertex of the waveform B come to rest, it ie results in Figure 3 "b with the dashed waveform A ¹ shown situation where the vertex t 'behind the apex t ^ waveform B lies.

Another difficulty with using edge detectors is that the reference level E must be precisely maintained. Looking at FIG. 3b it becomes clear that when the reference level E is shifted upwards, the vertex t is closer to the Vertex t ^ moves. Conversely, when the Reference level E the vertex t further from vertex t-, path.

FIG. 5 shows an embodiment of an Easter coverage detector 130 according to the invention, with which the problems which arise when using conventional, edge-sensing detectors are overcome. In the arrangement according to FIG. 5, two raster-related video signals, which correspond, for example, to signals Vo and V _& in FIG. 1 and are offset from one another according to FIGS. 4a and 4b, are coupled to the input terminals of two video gate circuits 10 and 12. A gate control signal G, which is derived from a line selector (not shown), activates gate circuits 10 and 12 and resets two flip-flops 18 and 20, all at a point in time t _Q , which is shown in FIGS. 4a and 4b. The activation of the gate circuits 10 and 12 causes the raster-related signals to appear at the outputs of these circuits, from where they arrive at one input of a respective associated comparator 14 and 16, respectively. The others

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Inputs of the comparators 14 and 16 are with a reference voltage Vg-rvp coupled, which is shown as level K in Figures 4a and 4t is. The output signals are therefore the comparators during operation 14 and 16 low "until the amplitudes of the input video signals A and B increase to a point where the Exceed reference voltage Vg-rm. At this point the output signals go the comparators 14 and 16 are high, which does not necessarily occur at the same time since the video signals as in the case of the Figures 4a and 4b can be shifted from one another. The outputs of comparators 14 and 16 that are high or low can be, are each to the input of an assigned flip-flop 18 or 20 and to an input of a respectively assigned Linking member 22 and 28 given. The output signals of the flip-flops 18 and 20 are each to an input a separate logic element 24 and 26 respectively. The other input of each of the members 26 and 24 is with the output a clock pulse generator 46 which operates, for example, at a nominal frequency of 100 MHz. The clock signal from the output of the clock generator 46 is also fed to one input each via a frequency divider (1: 2 divider) 48 which divides by 2 of the two link elements 22 and 28 given. The output signals of the logic elements 22 and 24 are ORed fed to the input of a counting circuit 30, while the output signals of the elements 26 and 28 in an OR operation the input of a counting circuit 34 are fed. the Outputs of counters 30 and 34 are assigned inputs an arithmetic logic unit 32 which, for example, add the count values stored in the counters 30 and 34 together or can subtract from each other in order to emme 0 at an output terminal the sum or the difference in the counters 30 and 34 display total accumulated counts.

The detector shown in FIG. 5 operates as follows: The video signal A is fed to the gate circuit 10, and at a time t _Q (shown in FIG. 4a) a gate control signal G appears, which activates the gate circuit 10 and sets the flip-flop 18. The output signal of the flip-flop 18 thus activates the

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kiiirprtinsBgl ^ Gl £ 4 _S the dca. iTskticp-ulsgefoer 46 sit the counter $ 0 couples »B9r hall 30 continues counting iron clock pulses fwt:" until ö £ 3 Tficl ^ o signal uin © amplitude equals ^ -pg »reached, ¥!" s of the ZsitdGHGs ? Όε ^τ ; 7 _ο latfeszams d ^ from tg "to t ^ la Figure 4a enfesr ^ isiito Usrs. Aio EGS ^ sspasaung" Pp ^ g. zxa time point txj ubersctei ^ \ ^: '5 :: ui3?' 3. ₅ Irving · '; - dsE ¹ ¥ epgleieSi @ 2? 14 das JFiipflop dasu, ssir; ^ "riir / '- asid su smL ^ sn- tjcmmcä the link 24 switched off and gltloJi-iv-Gl / lij- des 0-3 ied 22 switched on X" rii? D _{o the} latter couples d- ? a. '. '/ -ipulsa niit kslber Bplröfeeguena on the liagaag des Gäüiey:; i 5C ^: j ü2id 2! was about © 2? the duration "bzuo length dgs clie dera interval ■ '* .- -ίν iü ί / igOs 4a © atspsiclito 3sr counter 30 has now in its. Ii ^ -jtax ~ ?? ji eiü.s number gespsicfc.ss'to the same is the Siasiae of AnviAl ;! üS2?: Li 3'i-itiatervail "ö ^^^ appeared l'aktimpulse υ :; '" ύ? χ · ύ ":: 2, ί1ϊΓ. -; "®3? Is interval t ^ = t« ax halter T'akt & SGiiens er = schIκ- · ·.>, · ;;,:, I ^ uÜ3So £ a derzaJalsr uabs-sna der Zeitspaim® t ₄ = t _o with hai '-yy- - / jktx ^ e ^ -asaa bsu _o Rush cIse ¹ double period of the wälireiid der ZiJ.i. "- s ~ r \ rm.st _r . =» t.- ₃ Qiasslaufeaea Saktiapnls® counted Lat ₂ represents the Ge3-i2Lta ^ n1 i ~ Z2.LI & 2? 30 dea glsichea counting test represents ₀ how -we the counter JO tcz Scityiaal-t t «eis siaa ZeitDimkt t ait d®? glsicb =

ble Iber..l5ii i ^ -cöf ^ ecpssia gssälilt would have _o GoiEäß the

can in niatiissatisoiisffi? / lusäsraekswoiscs gQgükei '

i * - ¥ = ( Έ ° Asisahl d © r counting steps * Έ1 ) _s (1;

d _c = 7 ^# C? 3 number of counting steps d ₂ ) (2)

* ~ el

'2 = Y · ( Ύ <· number of sowing steps dp) 2
The distance from t «" to t ists

d _o
dt _a = CL ₁ -f - £, (3)

- 10 -

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"X 4

dt = V ° (ϊ - number of counting steps d. + V (4 number of ^{a! x} counting steps d ₂ )

In the above equations, V is the scanning speed of the

scanning beam and thus constant The quantity γ is also a Constant, where f is the frequency of the clock pulse generator. Therefore it can be written:

dt _e ^ number of counting steps d, - + number of counting steps d _o or:

dt £ Total number of counting steps in the counter.

Similarly, the video input signal applied to gate circuit 12 becomes B, which corresponds to the waveform in Figure 4b, with the comparator 16, the flip-flop 20 and the logic elements 26 and 28 evaluated in order to allow a total number to accumulate in the counter 34 which is equal to the temporal location or spatial position of the vertex t ^ of the video input signal B in Figure 4b is.

The counters now have a digital one in their respective registers A count is stored which represents the grid-related locations of the vertices t and t-u. The arithmetic logic unit 32

CL D

subtracts one count from the other to get at the output terminal 0 to supply a digital number which represents the spatial difference between the two rasters assigned to the video signals A and B. This digital number can, for example, be used directly in a microprocessor used as a control signal generator to generate the desired Control signal to be obtained, or it can be stored in a digital accumulator and passed through a digital-to-analog converter can be converted into a control signal. The output signal of the digital / analog converter can be applied to a DC control voltage which are in a closed control loop on the centering circuits of the raster-forming circuits 160 in Figure 1 can be fed back to the position of the grid relative

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to adjust to each other »

Up to this point, the detector according to the invention has only been described in connection with the horizontal haster centering, which takes place on the basis of a single vertical white bar in the reference pattern used as the test image 8 shows additional arrangements for the use of the detector according to FIG. 5 for sensing both the vertical and the horizontal grid coverage. The reference pattern shown in FIG. 6 contains two oblique white lines A and A ¹ , respectively. as seen by a first image pick-up device, and two oblique white lines B and B ¹ , as seen by a second image pick-up device are (horizontal and vertical misregistration) Detector according to FIG. 5 is used in the circuit according to FIG. 8 in the manner described below in order to determine the peaks of the video amplitude for locations f and g and for locations h and k on a reference line R and R ¹ , respectively, which at a time t _Q or t _Q 'for a common line begins. The horizontal displacement is then

e + e '

H «-2, (4)

and the vertical displacement is Tr e - e ¹

(5)

where e is the offset between the vertices of the video signals at f and g along the reference line R and e ^{1 is} the offset between the vertices of the video signals at h and k along the reference line R ¹ . The reference lines R and R ¹ lie on a common line.

FIG. 8 shows how the detector according to FIG. 5 is used for detection both the horizontal and the vertical displacement

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The one part of the arrangement shown in Figure 8 whose elements are labeled with the same numbers as in FIG. 5 operates in the same way as the arrangement according to FIG. 5 In FIG empfingt at its input reference signals ₅ which is a halation "a the vertical« = ^ and Hosisontals neteionsigaalea. of the IP television system and which derived a line control signal with the help of a known event divider. _{The line control signal can indicate S 9} B. the line Ir ₀ 128 of a certain part of the message ₉ if the reference pattern is in the range of the lütt® fies sasters !! © § ■ & _s like it "is shown at a in Figure 7 o the i? osa. The output of the Z @ ilsnwählers 50 row control signal supplied x-Jird on & @ n SSingang a monostafailen multivibrator 52 coupled Di © rising edge of the output signal of the multivibrator 52 t-Jisel · applied to an OR gate 5 ^ ₂ which comprises.! Gate control signal G as , cli ", o ®O2? scIia, lines 10 and 12 and at di © S st ζ input © the 2? lipflopg 'Ib imn, SO delivers» The Eückkippz © it dss mono stable © n SfelMviteQuC ^ a 25 is set in this way ₉ that the duration or lsbage of the Sorstanessigasla corresponds to the BSzrugs line HS ₉ that the cough of the seaslgüs Idnien A usd B intersects in - ^ igur 6 _o - While the B & mqt dos ÜJor control signal, the detector stores the counted falctiispulses is. The counters 30 and 5 ^ ₉ As described above la connection iiit Fig ^ s? 5 beseic? iebaa. wordea isto Asa & de of the Tossisuersignals ("bs-stiaiat by the monostable multivibrator 52) represents the atm appearing trailing edge of the output signal of the iaonostaMlen Hultivi'brator 52, which on the monostable multiv ibrator 56ς, the aonostable liultivibrator 42 and a data interlocking buffer 38 is coupled, the detector part of the arrangement according to Figure 8, so that it is the right side of the cough shown in Figure 6, ie the lines A 'and B' in the following manner queries. The leading edge of the output signal of the acoustic multivibrator 52 is used as a switch-on signal for the data locking buffer 38, so that the output of the arithmetic logic unit 32, which reproduces the size e in Figure 6 as a digital number, is held in the buffer 38 and at the terminal O ¹¹ for a further processing is available in the following manner.

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The output signal of the aonostable multivibrator 52 also triggers the monostable Hultryxbratör 42 ₉ whose output signal is sent to an OR gate 44 SHgsfufet iriz & cj which, in turn, tiit the backsetting of the Sänlss? JO -JBo 34- is connected ₀ to the counter for the next £ fessi2ia§ aii loseheso Di® BüeldriLppseit dss monostaMlen MältiriJrators 42 is set ₉ so that the arithmetic string 52 «Εά ά®5? SafcenYer-riegslungspiiffsE ¹ 38 sufficient Since Ziaben, ILASS operation gate of Sückstellung the counter to; eenaen ₃ ¥ i'5 above sr ^ SIiat ₃ x IIRD the output of the monostable en Iialtrribrato ^ s 52 auBsrdsa on the moaostalailea multivibrator fS <. re2; cppelt ₃ cLsssse. SüeMrippssit is eingsstsllt ₉ so that the renewed Srseugimg they E-srstsmsrsigaals Bi22? Chführung the measurement on the rssätss. 8'strbe d®s Eefarensaustsrs (lines A ^B and B ¹ in ZTieiir 6> · TsrssSger-'ö i-jisdo Hie bsi d © s? Hessimg on the left 3si- "s 232 Husts ^ s srseiig '?; äse aoaostsibil © Efelti ^ riteatos ¹ 58, der -: · ü "iiiissas-sasigaal des Boaostable Hultiviteators 5S gs = triggers ¥ ird, sin Migaagssisiual _s aess-sa lT © sd © rflaak® on the ODEE-G-Ii sd 54 g-sfcsppely ¥ 2j? do iüa HAD® of ¹ E3 @ ssi2ag on the side of the rscJatsa Ssfsrenz-QUE-sat liofsst ds :? aoaosta ^ il © HiaitiviDrator 58 a Sinschaltsigsial fiir sis. @ a. Batsa ^ / sr-risgelimsspiiffsr 36 ₀ with which the Result of the Hessimg ä & s SQehten S®ita ia di®sen Paffsr transferred i ^ iraj 30 da £ dsj? 2-ä'alWQs ^ ₀ dss ¹ ai® Large © ° (3? Igiar 6) in digital form represents ₉ to dei ¹ El @ iaa @ -3 " * ψ <§ ^ £ ηφ® £ made wirl _o equilateral, the signal of the aonostaMlds Eultiviteators 58 sets the counters JO - = jnd 54 via dsa iaoBOstaMlen Eiialti ^ ifeatoE ¹ 40 mad the OR element 4-4 surfick »On these ¥ © ise x-msß.en di © ¥ era measurements of the left and right yeast oyster laterally distributed over one and the same detector. The DateHV®s? Ri © g @ li2agspiaff © r 38 and 36 now contain the results of the liaken yad of the visible reference pattern, ie the sizes e and θ ^β ₀ Suroli © in © eieh subsequent processing (not shown) ₉ for example, a horizontal and a vertical correction signal is generated in a micropsoessor used for the control signal generator 140 or with the aid of a digital / analog XJmsetzungj according to equations (4) and (5) in order to correct the raster-forming Circuits 160 according to FIG. 1 for correcting the horizontal and vertical centering errors.

- 14 -

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It was described above, in particular in connection with FIG. 5 ", that the red signal V _{fi is} compared with the green signal Vg. And that the misregistration between these signals is corrected by means of a red / green difference signal for the blue signal by comparing this signal with the green signal and correcting the misregistration by means of a blue / green difference signal. Only two of the three grids, namely the red grid and the blue grid, require an adjustment compared to the green grid shown here plays the role of the reference grid.

FIG. 7 shows a reference pattern, with the aid of which both the horizontal and vertical centering errors as well as the width and height errors, the linearity errors, the Bhombus errors and the Rotation errors can be corrected so that a total grid coverage is achieved. As with the detector according to FIG Here, too, the line selector is set to issue certain line control signals, e.g. for the line in the case shown abc, the def line and the ghi line. Under control by an additional logic circuit arrangement, e.g. a microprocessor (not shown), the detector according to FIG. 8 can be operated in time division multiplex so that for each grid comparison the results of the measurement of the left and right sample parts at each of the positions a to i are stored in digital form in the memory and then mathematically processed by the microprocessor in digital form to generate control signals for all of the to generate the parameters mentioned above in connection with the total grid coverage.

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e e rs e

Claims (5)

Claims 1. Circuit arrangement for detecting the position of the peak amplitude a signal waveform having "leading and trailing edges" of substantially the same shape with a device for generating a reference level that intersects the leading and trailing edges of the signal curve by: a) a selection device (50) for supplying a reference time signal ("t"), which in time and position before is the position of the waveform; b) a first and a second clock generator (4-6, 4-8) for generating a first and a second reference frequency; c) a signal transmission channel (10, 14-, 18) with a cooling device (14 ·) which generates a key signal, when the waveform is above the reference level; d) a counting device (30), which with the first (4-6) and coupled to the second (48) clock and controlled by the reference timing signal and key signal will that they from the reference time signal to the periods of the first reference frequency for the key signal counts and counts the periods of the second reference frequency during the key signal, so that the total count the counter indicates the position of the peak amplitude of the waveform. 2. Device provided with a circuit arrangement according to FIG for correcting grid registration errors in a television camera, the at least two image recording devices and Contains facilities for the formation of associated television grids, who are in their position in relation to a common, - 16 - 909815/1082 28U333 can differentiate between scenes depicted on the image recording devices, characterized in that a) that a device (100) is provided in order to have a common Reference object (110) with a first and a second Insert border that the image recording devices for generating a first (A) or a second (B) raster-related signal caused; b) that the selection device (50) has at least one Selects television raster common line, which contains the raster-related signals, their amplitude the first limit rises to a peak between the first and second limits and from the peak slopes towards the second boundary; c) that the selection device (50) on the common 3 screen line a common reference time (tg) defines which is in time and position in front of the common reference object (110); d) that a second signal transmission channel (12, 16, 20) and a second counting device (34) are provided, to the positions of the peak amplitudes with the total count values of the first and the second counting device display the raster-related signals with respect to the common reference instant; e) that with the first (30) and the second (34-) counting device a processing device (140) is coupled which is derived from the difference in the count values of the counters obtains a control signal indicative of the difference in the position of the television rasters; f) that with the raster-forming device (160) a Correction means (150) is coupled, responsive to the control signal, for the difference in the raster position to diminish. 3. Device according to claim 1 or 2, characterized in that that the second reference frequency (f / 2) half as high as that 909815/1082 -17- first reference frequency (f). 4. Device according to claim 2, characterized in that the common reference object (110) is a sample image, which has at least one black bar on a white background. 5. Device according to claim 4-, characterized in that the Amplitude of the grid-related signals from the first boundary of the reference object to a peak value between the first and the second limit decreases and from the peak to the second Limit increases. 909815/1082